Red Dead Redemption -- Undead Nightmare Walkthrough & Strategy Guide

Rickets is hanging out at Casa Madrugada in eastern Mexico, and you can go meet up with him after you've cleaned Sepulcro's graveyard.

After you've talked to him, go do something else for a while, such as foraging for herbs to make more Zombie Bait. Return and give Rickets two Dynamite and two Zombie Bait. He will reward you with his own brand of artistic flair, teaching you how to manufacture Boom Bait. It's pretty much exactly what you think it is.